The present invention generally relates to a method and apparatus for coating a substrate with a liquid resin, and, more particularly, to a method and apparatus for coating selected portions of a rigid or non-rigid substrate with predetermined thicknesses of a liquid resin to form an outer layer for the substrate.
In many applications, it is desirable to provide a relatively thin, outer layer or skin for a substrate. Substrate as used herein will broadly refer to an underlying structure or part, both rigid and nonrigid. The substrate may include a plurality of components, some rigid and some nonrigid. The layer or skin may perform a variety of functions such as protecting the substrate from adverse external conditions, providing the external surface of the substrate or portions thereof with characteristics suitable for particular applications, providing an aesthetically appealing finished product, and the like. The outer layer or skin may also improve the tear resistance of the substrate and enhance overall strength providing a more durable and rugged finished product. A conducting wire surrounded by an insulating layer is one example of a substrate having an outer layer performing such functions. Another substrate which may include an outer layer or skin is a weatherseal. The present invention will be discussed below in terms of a weatherseal. However, the method and apparatus of the present invention are not limited in this respect. The present invention is broadly applicable where it is desired to provide an outer layer or skin for rigid and non-rigid substrates including, but not limited to, foams, metals, and extrudable plastics.
In general, weatherseals seal joints or spaces between doors and windows so as to inhibit infiltration of air, rain, snow, and other elements. Effective weatherseals can reduce both heating costs in winter and cooling costs in summer. Certain characteristics are necessary to produce an effective weatherseal. First, a weatherseal should have good compression set resistance. Compression set resistance refers to the ability of a material to resume its initial shape after being subjected to a compressive load. Failure to resume this initial shape may result in an uneven seal and reduce the effectiveness of the weatherseal. Second, a weatherseal should be soft and yielding, i.e., it should be easily compressible and conform to irregular surfaces. The gaps in doors, windows and the like in which weatherseals are utilized differ in size due to construction and a good weatherseal should have sufficient compressibility to conform to a wide range of gap sizes. Compressibility also ensures that a door or window, for example, can be closed without excessive force and still compress the weatherseal sufficiently to form the necessary seal.
The prior art discloses many materials which are utilized as weatherseals. U.S. Pat. Nos. 4,328,273 and 4,185,416 disclose the use of urethane foams for a weatherseal. Commonly assigned co-pending Application Ser. No. 121,805, incorporated herein by reference, discloses the use of a low density foamed thermoplastic elastomer for a weatherseal. However, these and similar materials generally have high coefficients of friction and may be easily damaged. Thus, their effectiveness and utility as a weatherseal is reduced. These problems are magnified where the weatherseal is subjected to sliding contact or other abrasive forces, as in the aforementioned U.S. patents.
In order to alleviate these problems, an outer layer or skin is typically provided for the weatherseal. The outer layer generally has a low coefficient of friction relative to the surface of contact to facilitate relative motion and is flexible to permit compression of the underlying seal. The outer layer also protects the seal from rips and tears caused by sliding contact or other abrasive forces. Low friction materials such as polyethylene copolymers, polyvinylchloride, and polypropylene copolymers have been utilized in the prior art for this outer layer.
However, there are several disadvantages associated with providing these low friction outer layers. Attaching the outer layer to the underlying seal may require a separate manufacturing step and increase the labor required to make the seal. This increases labor costs. If the outer layer is applied as a crosshead extrusion to the weatherseal, orientation of the outer layer during "draw-down" onto the seal creates low resistance to tears along the length of the seal. Thus, an initially small tear in the outer layer can propagate into a much larger tear, adversely affecting the effectiveness and utility of the weatherseal. Additionally, crosshead extrusion apparatus generally requires complex arrangments of equipment and expensive dies. These factors also increase production costs.
One prior art technique provides an outer skin for a substrate by melting a resin and placing the melted resin in a tank or pool with an entrance opening and an exit opening. The substrate is then pulled or dragged through the melted resin. The exit opening serves as a doctor blade to configure the outer layer. However, it is difficult to precisely control the thickness of the outer layer or to selectively coat portions of the substrate utilizing this prior art technique. Also, it is difficult to provide an outer layer of varying thickness. Finally, the pressure and drag exerted on a non-rigid substrate such as a foam by a viscous melted resin deforms and stretches the non-rigid substrate and generates a low quality product.